The heating furnace has conventionally been used for heat treating a treatment object such as steel slab. The heating furnace employs the combustion burner for mixing the fuel supplied through the fuel supply pipe with the combustion air supplied through the combustion air supply pipe and burning the fuel inside a furnace.
A continuous heating furnace has also been used as such a heating furnace. The continuous heating furnace includes a plurality of the combustion burners arranged in a longitudinal direction thereof such that the treatment objects are continuously heat treated while sequentially moved through the inside of furnace in the longitudinal direction.
Such heating furnaces have the following problem. When the treatment objects such as steel slabs are heat treated in the heating furnace, scales are generated by oxidation of the treatment objects. The scales fall and gradually accumulate in the furnace. This leads to a need for maintenance work on the heating furnace by a worker who enters the inside of the furnace for removal of the scales and the like.
To allow the worker to enter the inside of the furnace for maintenance work of the heating furnace, the temperature in the furnace must be lowered to a level suitable for working.
In the practice of the art, the temperature in the furnace is lowered to the level suitable for working as follows. While stopping the combustion by cutting off the fuel supply through the fuel supply pipe, a blower is driven to feed a cooling air to the inside of furnace via the combustion air supply pipe such that the inside of furnace is cooled by the cooling air.
In the case where the cooling air is fed to the inside of furnace through the combustion air supply pipe so as to cool the inside of furnace, however, quite a long time is taken before the temperature in the furnace is lowered to the level suitable for working. Particularly, such a long time as a few days is taken in the case of the continuous heating furnace where the plural combustion burners are arranged in the longitudinal direction thereof and where the treatment objects are continuously heat treated while sequentially moved through the furnace in the longitudinal direction.
Heretofore, Patent Document 1 has disclosed a heating furnace which includes spray nozzles disposed at a ceiling and the like of the furnace in a manner to be insertable in the furnace. The heating furnace is adapted to lower the temperature in the furnace by stopping the combustion in the heating furnace, followed by feeding the cooling air to the inside of furnace as described above while inserting the spray nozzles in the furnace for spraying water from the spray nozzles onto the scales accumulated in the furnace. Further, disclosed in Patent Document 2 is a heating furnace which includes atomizing nozzles and spray nozzles similar to those of Patent Document 1 disposed at the ceiling and the like of the furnace in a manner to be insertable in the furnace. The heating furnace is adapted to lower the temperature in the furnace by stopping the combustion in the heating furnace, followed by feeding the cooling air to the inside of furnace as described above, while inserting the atomizing nozzles and spray nozzles in the furnace for spraying atomized cooling water in the furnace from the atomizing nozzles and spraying the water from the spray nozzles onto the scales accumulated in the furnace.
As stated in Patent Documents 1 and 2, however, the work of installing the spray nozzles or atomizing nozzles in the ceiling and the like of the heating furnace in the manner that the nozzles are insertable in the furnace is quite cumbersome and costly. Particularly, in the continuous heating furnace where the plural combustion burners are arranged in the longitudinal direction thereof and the treatment objects are continuously heat treated while sequentially moved in the longitudinal direction, a larger number of spray nozzles and atomizing nozzles are required so that the installation work takes a larger amount of time and increased costs.
In the case where the spray nozzles and the atomizing nozzles are disposed in the furnace in a manner to be insertable in the furnace, the spray nozzles and atomizing nozzles need to be inserted in the furnace each time. The work is extremely complicated and time-consuming. Furthermore, doing the work at a high-temperature area near the ceiling right after stopping combustion is highly risky. Further, in such heating furnaces where the treatment objects are heat treated therein by burning the fuel by the above-described combustion burners, it is necessary to block up mounting parts of the spray nozzles and atomizing nozzles with a cover material or the like so as to prevent heat in the furnace from leaking through the mounting parts of the spray nozzles and atomizing nozzles. This involves extremely cumbersome work. What is more, it is impractical to reliably prevent the heat leakage through the mounting parts or the cover material. There is also a problem concerning the decrease in thermal efficiency of the heating furnace.